1. Field of the Invention
The present invention relates to an external prosthesis, and more specifically to a valve system for air release from a limb prosthesis.
2. Related Art
Gravitational and other forces tend to cause separation between a prosthetic limb and a residual limb. This happens, for example, during the swing phase of the gait, when a prosthetic leg is additionally subjected to centrifugal forces. The manner in which an artificial limb is suspended and/or attached to the residual limb determines the amount of control an amputee has over the prosthesis. Patients have routinely worn a variety of belts, straps, cuffs and harnesses to prevent the prosthetic limb from separating from the residual limb, but such devices are inconvenient and tend to cause chafing against the patient's body, giving rise to sores and abrasions.
It has long been appreciated that differential air pressure or “suction” may be utilized to retain or suspend, or assist in retaining or suspending, a prosthetic limb on a patient's residual limb. Suction suspension typically involves a hard socket and a cooperating liner positioned between the residual limb and the prosthetic socket. The liner is rolled onto the residual limb for a suction, slight compression, and/or gripping connection of the inner gel layer (or otherwise tacky layer) of the liner to the skin of the residual limb. The liner-covered limb is then inserted into the prosthetic socket, and the outer surface/layer of the liner preferably forms a suction, grip, or other interference fit to the socket to interfere with the socket falling off the limb.
These socket liners frequently have been called “suction liners,” “gel liners,” “roll-on liners” or “suspension liners” and include the “first generation” of gel-layer-only liners, and also the modern “second generation” of multiple-layer liners currently preferred by most wearers of prosthetics. These modern liners comprise a thin textile/fabric outer layer that is fixed to the gel-like inside layer. Thus, the second generation of liners is similar to the first in its connection to the residual limb, but its connection to the socket is modified by the presence of the textile/fabric layer. The term “suction liner” began with the first generation liners, which featured the gel layer contacting both the residual limb (liner's inner surface) and the socket (liner's outer surface), and which, therefore, could be used to create a fairly high amount of pressure differential between the inside of the socket (in the “well” of the socket) and the surrounding ambient air. The terms “suction liner” and “suction socket” are still used by many manufacturers, prosthetic technicians, insurance and medicare/medicaid entities, and wearers of prosthetics, even though the modern liners, with their textile/fabric outer layers, typically do not form what would be called “true” or “pure” suction with the socket, as further discussed below. See the discussion of suction liners in Janusson, et al. (U.S. Pat. No. 6,706,364) and Janusson, et al. (U.S. Pat. No. 6,626,952).
Socket liners are usually fabricated to be, or to include an inner layer of, silicone, urethane, or other gel-like material that grips the limb to such an extent that they need to be rolled-onto the limb from a rolled-up “doughnut” form, rather than pulled on like a sock. When rolled-on, there is little, if any, air remaining between the inner surface of the roll-on liner and the limb, and the roll-on liner is snug against the limb all the way around the circumference of the limb. Also, the inner surface of the roll-on liner is of such material and tacky texture that air will not be able to, or be very unlikely to, enter between the roll-on liner and limb. Thus, the roll-on liner may be said to form a suction fit and/or a slight compression fit with the limb. A distal force on the liner, such as caused by the swing of a gait with a prosthetic leg, may tug on the roll-on liner but typically does not loosen, lower, or remove the liner from the limb.
The hard socket is usually laminated or otherwise fabricated from polyethylene, polypropylene, or other copolymers, for example, and is donned over the liner and the residual limb. A suction-fit, including a partial-suction fit, as discussed above, may form between the liner-sheathed limb and the interior of the socket. A “true” suction fit (allowing high suction, greater amount of vacuum) will be more likely to form if 1) the liner exterior surface is smooth and flexible enough to conform to the contours of the residual limb, for example, non-air-permeable material such as the silicone, urethane, or other rubbery or gel-like material such as described above for the liner-to-limb connection; 2) if the interior surface of the socket is also smooth and non-air-permeable; and, of course, 3) if the socket has no un-sealed holes or apertures.
A “partial” suction fit (allowing lower suction, low amount of vacuum) is more likely to form if one of the above three conditions is not met, for example, if the outside of the liner is the thin fabric or other woven material bonded to a rubbery/gel-like interior layer of the liner, for example, as described above for “second generation” liners. In such a case, some air will tend to leak through or past the fabric layer of the modern liners into the well of the socket, that is, between the liner and the socket interior surface, so that there is typically not a true air-tight seal between the two. However, the air leaks fairly slowly because of the preferred close fit between the contour of the liner-cover limb and the contour of the internal surface of the socket. This slow air leakage and close fit typically allow their to be a “partial” suction fit between the socket and the liner outer surface, and this “partial” suction fit tends to be more comfortable for many wearers that a “true” or “full” suction fit. In other words, a textile/fabric-covered liner and the resulting “partial” suction tends to be more comfortable than the stronger “tugging” on the residual limb created by the “full” suction of first generation, gel-layer-only liner. The air that slowly leaks into space(s) in between the socket and the liner tends to be expelled with each step due to the force of the residual limb pushing into the socket. This way, modern, fabric-covered roll-on liners still tend to create some pressure differential between the well of the socket and the ambient air.
Therefore, many of skill in the field of prosthetics still apply the term “suction” to a fit or suspension of the prosthetic to the limb ranging from excellent suction (with a “true” seal, large resistance to equalization of pressure between the inside and the outside of the socket) to slight suction (with a “partial” seal, small resistance to said equalization such as in many popular liners). Therefore, the terms “suction,” “suction-fit,” and “suction suspension” herein are therefore not limiting to a particular amount of pressure differential, but to the general process known well in this field of providing a “roll-on” liner or other “interference” liner that helps keep a socket on a residual limb while creating at least a small amount of blockage/hindrance to air freely moving in and out of the socket well past the residual limb.
Therefore, it may be said that any region or amount of negative pressure in the space(s) between the liner-sheathed stump and the interior of the socket, relative to ambient (outside of the socket), may help to hold the prosthesis upon the limb during use. Certainly, more suction is more secure than slight suction, but there may be comfort sacrifices that result from more suction, for example, chaffing or pulling on the limb. A high-suction prosthesis suspension system may cause the user a discomforting disturbance of circulation in the limb on which the prosthesis is worn, due to the build up of a high amount of partial vacuum during walking, particularly in warm humid weather. Therefore, a very popular conventional roll-on liner is one such as the Ohio Willow Wood Alpha™ liner, which has multiple layers, that is, a rubbery/gel-like inner layer and a thin fabric outer layer bonded to the inner layer, so as to moderate the suction to a reasonably effective amount without allowing the great forces on the limb that can result from a high amount of suction. A “suction liner” or “roll-on liner” suspension, even in moderate range of suction provided by the preferred liners, gives the patient the ability to better control the prosthesis and provides for useful sensory or proprioceptive feedback. This is because there is a more intimate connection between the limb and the prosthetic, over much of the surface area of the limb, compared to old-fashioned waist belts, distal locks, or other methods. Suction or roll-on liner suspension also make a prosthesis feel lighter as compared to other forms of suspension.
A valve system may be used in combination with a suction/roll-on suspension system in order to regulate the air pressure in the socket, so that undesirable pressure differentials do not prevent or complicate the donning and doffing of the socket. Conventional valves aim at relieving buildup of pressure when the lined limb is inserted into the socket, which is typically a snug fit by design, to prevent a positive pressure inside the socket relative to outside of the socket (ambient air) and therefore to allow donning.
Because the typical valve system is a one-way valve, or “check valve,” it is intended to maintain a slight negative pressure (slight, partial suction) relative to ambient once the socket has been fitted on the residual limb and used. The process of walking and other weight-bearing will tend to push the limb further into the socket, but the swing of the gait will tend to pull the socket off the limb. The pushing of the limb further into the socket may cause the valve to allow air to be expelled, and the pulling of the socket during the swing will tend to create suction in the socket because the valve will not allow air to enter through the valve.
In applications wherein the multi-layer roll-on liner allows air to slowly leak into the socket well, or wherein a seam, connection, lock or other aperture in the socket allows air to leak into the socket, weight-bearing steps will tend to expel air from inside the socket through the valve and then said leaking will tend to replace at least some of it (especially on the swing of the gait). Therefore, there may be frequent opening and closing of the valve, perhaps for each, or for many, of the user's steps. Many conventional valves for these applications are known to either not work very well, to plug easily, or to make embarrassing noise with each step.
There are many valve systems in use in the market. Typical valve systems use an inner base that resides inside of the socket and passes to the outside of the socket. The outer housing and the valve are then threaded onto the inner base or threaded to the socket wall in an attempt to create an air-tight seal. Such systems requires a generally flat socket wall surface for installing the valve and outer base to prevent air from leaking around the valve structure and out of the socket instead of being expelled through the valve at the desired air pressure.
Issued patents and patent publications relating to valve systems are listed as follows: Underwood (U.S. Pat. No. 1,586,015), Catranis (U.S. Pat. No. 2,530,285), Sharp et al. (U.S. Pat. No. 2,533,404), Hauser (U.S. Pat. No. 2,790,180), Edwards (U.S. Pat. No. 4,010,052), Carrow (U.S. Pat. No. 4,106,745), Greene (U.S. Pat. No. 5,201,774), Hill (U.S. Pat. No. 5,490,537), Hill (U.S. Pat. No. 5,709,017), Slemker et al. (U.S. Pat. No. 6,287,345), Perkins (U.S. Pat. No. 6,334,876), Hoerner (U.S. Pat. No. 6,361,568), Caspers (U.S. Pat. No. 6,508,842), Laghi (U.S. Pat. No. 6,544,292), Caspers (U.S. Pat. No. 6,761,742), Abrogast et al. (U.S. Pat. No. 6,797,008), Caspers (U.S. Publication No. 2004/0181290), and Patterson et al. (U.S. Publication No. 2004/0260403).